Patent Document 1 discloses a control device of a variable valve timing apparatus that changes rotational phase of a cam shaft with respect to a crank shaft to change a valve timing by adjusting a rotational speed of a motor based on a half rotational speed of a rotational speed of the crank shaft.
In this control device, every time a cam angle signal is output from a cam angle sensor, a measured value of a valve timing is obtained based on the cam angle signal and a crank angle signal output from a crank angle sensor, and a change amount of the valve timing is obtained based on a difference between a rotational speed of a motor and a half value of a rotational speed of a crank shaft in a predetermined calculation period so that a final measured value of the valve timing is calculated based on the measured value of the valve timing and the change amount of the valve timing.